1. Technical Field
The present disclosure relates to composites, particularly, to a carbon nanotube composite, a method for making the same, and an electrochemical capacitor using the same.
2. Description of Related Art
Carbon nanotubes (CNT) are a novel carbonaceous material having extremely small size and extremely large specific surface area. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties, and have been widely used in a plurality of fields such as emitters, gas storage and separation, chemical sensors, and high strength composites.
However, the main obstacle in applying carbon nanotubes is the difficulty in processing the common powder form of the carbon nanotube products. Therefore, forming separate and tiny carbon nanotubes into manipulable carbon nanotube structures is necessary.
Recently, as disclosed by Jiang et al., Nature, 2002, vol. 419, p801, Spinning Continuous CNT Yarns, a free-standing carbon nanotube yarn has been fabricated. The carbon nanotube yarn is directly drawn from a carbon nanotube array. The carbon nanotube yarn includes a plurality of carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes are substantially parallel to an axis of the carbon nanotube yarn. However, the mechanical strength and toughness of the carbon nanotube yarn is not relatively high.
It is becoming increasingly popular for CNTs to be used to make composite materials. Composites of carbon nanotubes and metals, semiconductors, or polymers resulting in material with qualities of both materials used in the composite. Often, the method for producing a carbon nanotube composite includes a stirring step or vibration step to disperse carbon nanotube powder in the composite matrix. However, carbon nanotubes have extremely high surface energy and are prone to aggregate. Therefore, it is very difficult to achieve a composite with carbon nanotubes evenly dispersed therein.
An electrochemical capacitor using carbon nanotubes has been disclosed by Chunming Niu et al., High power electrochemical capacitors based on carbon nanotube electrodes, Apply Physics Letter, vol 70, p1480-1482 (1997). An electrode film of the electrochemical capacitor is formed from carbon nanotube powder. However, the carbon nanotube powder is prone to aggregate during the formation of the electrode film. The aggregated carbon nanotubes negatively impact desirable properties of the electrochemical capacitor.
What is needed, therefore, is to provide a carbon nanotube composite with improved tensile strength and Young's modulus, a method for making the same and avoiding aggregation of the carbon nanotubes used, and an electrochemical capacitor using the same with relatively high power density and energy density.